This invention relates to voltage controlled crystal oscillators, and in particular, to cost-effective packaged modules providing at least two different and relatively high-frequency oscillator outputs.
High capacity data networks rely on signal repeaters and sensitive receivers for low-error data transmission. To decode and/or cleanly retransmit a serial data signal, such network devices include components for creating a data timing signal having the same phase and frequency as the data signal. This step of creating a timing signal has been labeled xe2x80x9cclock recovery.xe2x80x9d
Data clock recovery requires a relatively high purity reference signal to serve as a starting point for matching the serial data signal clock rate and also requires circuitry for frequency adjustment. The type, cost and quality of the technology employed to generate the high purity reference signal varies according to the class of data network application. For fixed large-scale installations, an xe2x80x9catomicxe2x80x9d clock may serve as the ultimate source of the reference signal. For remote or movable systems, components including specially configured quartz resonators have been used. As communication network technology progresses towards providing higher bandwidth interconnections to local area networks and computer workstations, the need has grown for smaller and less-expensive clock recovery technology solutions.
For many clock recovery applications, the reference signal generator must be adjustable, i.e., controllable, over a precisely defined operating curve. This adjustability requirement is conveniently defined as an Absolute Pull Range (APR). APR is defined as the controllable frequency deviation (specified in xc2x1ppm) from the nominal frequency (F0) over a wide range of operating parameters, including supply voltage variations, temperature variations, output load variations, and time (i.e., aging). Clock recovery may require controllable oscillators having both a minimum and a maximum APR.
A typical optoelectronics system includes numerous line cards and a backplane. Frequently the end use of a particular system is not determined until a specific customer request is known. For example, a line card could be for a SONET application (622.08 MHz) or for a Gigabit ETHERNET application (644.531 MHz). Therefore, optoelectronic line cards that are compatible with more than one communication standard offer manufacturers both an overall cost-of-production and a marketing advantage. If the desired final frequency could be implemented with just a software command after the system has been constructed, the flexibility of the system would be greatly enhanced.
Recent revisions made to optical communication standards endorse forward error correction (FEC) techniques. To implement FEC techniques, optoelectronic systems must be able to operate at a standard communication frequency (e.g., SONET 622.08 MHz) and also one of the common forward error correction (FEC) frequencies, 666.514 MHz or 669.326 MHz. A dual range VCXO or a dual range reference clock or one of each type would be advantageous for this reason.
Accordingly, network device manufacturers, especially those working with optical systems, desire multiple high-performance oscillators in the same assembly at reduced sizes and low cost.
The present invention offers a solution to the two-frequencies requirement by providing a dual-range oscillator module in a cost-effective, reduced footprint package. The dual-range oscillator modules comprise an upper and a lower wiring board panel, an upper set of crystal oscillator components mounted to a component side of the upper wiring board panel, a lower set of crystal oscillator components mounted to a component side of the lower wiring board panel, and a side-wall frame including a plurality of conductors for providing connections between input-output contacts of the upper wiring board panel and the input-output contacts of the lower wiring panel.
Each wiring board panel has a component side, a surface mount side, a central portion and an outer edge portion that includes a plurality of input-output contacts. The lower set of crystal oscillator components is mounted to the component side of the lower wiring board panel such that the lower set of components and the lower wiring board panel together define a first crystal oscillator circuit. The upper set of crystal oscillator components is mounted to the component side of the upper wiring board panel such that the upper set of components and the upper wiring board panel together define a second crystal oscillator circuit.
The side-wall frame is set between the upper and the lower wiring board. The side-wall frame includes a plurality of conductors linking the input-output contacts of the upper wiring board panel and the input-output contacts of the lower wiring panel.
There are other advantages and features of this invention which will be more readily apparent from the following detailed description of the preferred embodiment of the invention, the drawings, and the appended claims.